1. Field of the Invention
The present invention relates generally to tubular prostheses, such as grafts, stents, stent-grafts, and the like. More particularly, the present invention provides endoluminal prostheses having discrete position indicating elements which facilitate orienting and deploying the prostheses within body lumens, particularly within branching blood vessels for the treatment of abdominal and other aneurysms.
Vascular aneurysms are the result of abnormal dilation of a blood vessel, usually resulting from disease and/or genetic predisposition, which can weaken the arterial wall and allow it to expand. While aneurysms can occur in any blood vessel, most occur in the aorta and peripheral arteries, with the majority of aortic aneurysms occurring in the abdominal aorta, usually beginning below the renal arteries and often extending into one or both of the iliac arteries.
Aortic aneurysms are most commonly treated in open surgical procedures, where the diseased vessel segment is bypassed and repaired with an artificial vascular graft. While considered to be an effective surgical technique, particularly considering the alternative of a usually fatal ruptured abdominal aortic aneurysm, conventional vascular graft surgery suffers from a number of disadvantages. The surgical procedure is complex and requires experienced surgeons and well equipped surgical facilities. Even with the best surgeons and equipment, however, patients being treated frequently are elderly and weakened from cardiovascular and other diseases, reducing the number of eligible patients. Even for eligible patients prior to rupture, conventional aneurysm repair has a relatively high morality rate, usually from 2% to 10%. Morbidity related to the conventional surgery includes myocardial infarction, renal failure, impotence, paralysis, and other conditions. Additionally, even with successful surgery, recovery takes several weeks, and often requires a lengthy hospital stay.
In order to overcome some or all of these drawbacks, endovascular prosthesis placement for the treatment of aneurysms has been proposed. Although very promising, many of the proposed methods and apparatus suffer from undesirable limitations. In particular, proper positioning of an endovascular prosthesis within the vascular system can be problematic.
Accurately positioning and orienting endoluminal prostheses is critical to the efficacy of endovascular aneurysm therapies. These tubular prostheses are generally introduced into the vascular system within a catheter and in a radially compressed configuration, typically being maneuvered into position under fluoroscopy. The positioned prosthesis will radially expand, preferably engaging and sealing against the endolithium of the healthy vessel wall both upstream and downstream of the weakened, distended aneurysm. The prosthesis may expand resiliently when released from the catheter, or may be mechanically expanded, typically using a balloon catheter. In either case, the prosthesis will preferably span the entire aneurysm to prevent pressure from acting on the weakened lumenal wall, and to prevent leakage through any rupture of the aneurysm. To provide these advantages, the prosthesis must be axial positioned accurately across the aneurysm so as to isolate it from the blood flow through the prosthetic lumen.
Proper radial orientation of endoluminal prostheses is also important, particularly when deploying branching and asymmetric prostheses within the tortuous vascular system. If the branches of branching prostheses are not oriented toward their respective branching body lumens, the surrounding body lumen may be distended to adapt to the misaligned prosthesis, or the prosthetic lumen may be distorted or even closed entirely. For example, if the trunk of a bifurcated prosthesis is deployed with a branch oriented 90.degree. from the iliac arteries (i.e., angling dorsally rather than laterally), the prosthetic branch lumen may fold or kink, and will have to at least bend at a sharp angle to enter the laterally oriented iliac. In fact, as branching prostheses are often assembled in situ, it may not be possible to introduce the branch prosthesis into such a misaligned branch port. As recapture or repositioning of expanded endoluminal prostheses is often problematic, it may even be necessary to resort to an emergency invasive procedure to remedy such misalignment.
Tubular endovascular prostheses are often formed as stent-grafts having a flexible tubular liner or "graft" which is supported by a perforate tubular frame or "stent". The frame perforations define radially expandable structures, while the frame often include metals which are, to some extent, visible under fluoroscopy.
To facilitate positioning of endovascular prostheses, it has previously been proposed to coil gold or platinum wires around an element of the perforate frame structure to enhance the visibility of the prosthesis under fluoroscopy. Similarly, it has been suggested that a tube be crimped over an element of the frame. Unfortunately, affixing such structures to the frame may limit or interfere with the radial compressibility of the prosthesis. It can also be difficult to identify the portion of the frame having an enhanced image against the backdrop of the frame itself, and to orient the prosthesis properly based on one or more enhanced frame arms.
Alternatively, it has been suggested to affix radiopaque lines or image markers to bifurcated grafts in the form of fine wire or chain, either woven into the cloth or applied after weaving, or as an inert paint or plastic. However, the liners of endoluminal prostheses must remain highly flexible, typically being folded when the prosthesis is compressed and unfolding during deployment. Wires, chains, or paints which are sufficiently flexible will generally provide only limited-contrast images when the graft is supported by the obscuring frame, and may become detached from the prosthesis once deployed in the body lumen, with potentially catastrophic consequences. Moreover, imaging of such thin, flexible, low-contrast markers is particularly difficult when the prosthesis is in the high density, radially compressed configuration and disposed within a catheter, as is generally required for intravascular maneuvering.
For these reasons, it would be desirable to provide improved endoluminal prostheses and methods for their use. It would be particularly desirable to provide endoluminal prostheses having high-contrast orientation indicating imaging markers which do not interfere with radial compression or expansion, and which are securely and reliably attached to the prosthesis. It would further be desirable if such markers could clearly indicate both the position and orientation of the prosthesis, ideally while the prosthesis remains compressed in the delivery catheter, but without substantially increasing the size of the delivery system.
2. Description of the Background Art
Co-pending U.S. patent application Ser. No. 08/538,706, filed Oct. 3, 1995, the full disclosure of which is hereby incorporated by reference, describes modular prostheses and prosthetic construction methods. Provisional Application Serial No. 60/008,254, filed Dec. 1, 1995, also incorporated herein by reference, describes bifurcated modular prosthetic structures and in situ methods for their assembly.
Published PCT patent application WO 95/21,592 describes a bifurcated endoluminal prosthesis including a bifurcated stent and a second stent. One or more X-ray opaque coils or tubes may de disposed over an arm of the stent structure so that the stents can be aligned and engaged in situ under X-ray monitoring. U.S. Pat. No. 5,387,235 describes a bifurcated graft having radiopaque lines and markers formed of fine wire or chains of inert metal, or of an inert paint or plastic.